The objective of this research is to develop a better understanding of molecular processes responsible for electrical excitability. Studies will be pursued on the biochemical characterization of a voltage-regulated sodium channel which is responsible for the early sodium currents of the action potential. The goals are to resolve the structure of the sodium channel molecule, and to relate the structure to the voltage-dependent regulation of ion transport. Specific neurotoxins, including tetrodotoxin (TTX) and saxitoxin (STX) serve as biochemical markers for the channel in membranes and detergent solubilized preparations. It has been possible to solubilize, stabilize and isolate a TTX and STX binding protein from the electoplax membranes of Electrophorus electricus. The structure and composition of the isolated protein, as prepared by procedures currently established, and by improved methods to be developed in the laboratory, will be determined. Also, attempts will be made to prepare osmotically intact, right-side-out membrane vesicles from the electroplax. These will be derived exclusively from the innervated face of the cell and are expected to be highly enriched in the sodium channel. These would be useful for demonstrating sodium channel mediated ion transport, for neurotoxin binding studies, and may permit demonstration of voltage-dependent activation of transport. Such membranes would provide an excellent starting material for rapid conventional or affinity purification procedures. This would minimize the time for isolation and reduce the possibility that the molecule has been dissociated or degraded. The possibility of demonstrating that the channel is physically and pharmacologically well behaved in the membranes would provide improved confidence that the isolated structure is undegraded. If the isolation procedures are rapid and can be performed on analytical scale, it may be possible to chemically modify the channel while still in the membranes and subsequently isolate and determine the site and extent of modification. In this way it may be possible to begin to relate the structural features of the molecule to its function.